Cumene hydroperoxide (hereinafter “CHP”) is commonly produced using one or more well known methods of oxidation of cumene with air oxygen at a high temperature, i.e., oxidation takes place in liquid-gas system. Typically, cumene is oxidized until CHP concentration reaches 20-35 wt. %, because further increase in cumene conversion leads to a significant build-up of by-products resulting in a proportionally lower process selectivity. The oxidation products are then delivered to a vacuum stripping stage where un-reacted cumene is distilled. The stripping bottom product containing about 60-93 weight percent of CHP is then delivered to a CHP cleavage stage, where CHP decomposes into acetone and phenol under influence of an acidic catalyst. It is well known that in conventional oxidation processes, the main CHP formation reaction is accompanied by a number of side reactions.
The effect of side reactions on the main CHP formation reaction depends, among other factors, on process conditions such as one or more of the following: temperature, product residence time in the reactors, and cumene conversion degree. Typically, the main by-products formed in the side reactions are dimehtylbenzene alcohol (hereinafter “DMBA”), acetophenone (hereinafter “AP”) and organic acids, such as formic acid, acetic acid, and/or benzoic acid. Formic and benzoic acids serve to catalyze the acidic decomposition of CHP to form phenol and acetone.
The presence of phenol in the reaction products, under the conditions of a radical oxidation process, is extremely undesirable because it results in a dramatic inhibition of the CHP formation reaction and has a significant negative impact on the overall process selectivity. Other inhibitors of CHP formation reaction (such as sulfur-containing trace contaminants, etc.), that may be present as a result of utilization of lower-grade cumene, also have a considerable negative effect on the process.
In fact, research has demonstrated that when employing conventional previously known process technologies, (i.e. without special treatment of the cumene oxidation products with ammonia), the rate of oxidation of low-quality cumene (in which sulfur-containing trace contaminants are present) is so slow that such conventional technologies could scarcely be considered acceptable for commercial processes. Moreover, when the CHP concentration reaches about 20 wt. %, the conversion of cumene starts to decrease, which leads to complete termination of the reaction. The undesirably low rate of reaction at the initial period is a result of the presence of inhibitors that are contained in the cumene, (most commonly, sulfur-containing contaminants). Specifically, the reason for the inevitable slow-down of the oxidation rate over a course of time, is the joint influence on the reaction of inhibitors accumulated in the reactor due to the oxidation reaction itself, as well as inhibitors introduced with fresh cumene. In fact, the rate of formation of radicals in the reactor turns out to be slower than the rate of the radical chain propagation, which leads to the suppression of the process.
The above-incorporated MPCH Application describes a number of previously known attempts to solve the above-described problem. One specific previously known approach to combating the very strong influence of inhibitors present in conventional commercial processes employing low-quality cumene, involves simultaneous use of the following techniques: (1) adding a sufficiently large amount of caustic to the reactor in which the reaction is taking place, and (2) elevating the temperature in the process reactor(s). However, this attempt to deal with the undesirable impurities has the extremely high price of low selectivity of cumene conversion to CHP (85-89 mol. %), and also a low value of cumene conversion (16-18%). As a result, technical CHP produced in the above-described manner, contains 7-9 wt. % of DMBA and 1.6-2.0 wt. % of AP, by-products which predetermine an extremely low selectivity of the cumene oxidation process and phenol process on the whole.
The above-incorporated MPCH Application provides an excellent solution to the problem of dealing with oxidation reaction inhibitors present in cumene to greatly improve process selectivity. Specifically, the MPCH Application disclosed a continuous method of cumene oxidation in a gas-liquid system, where the liquid phase is represented by cumene and its oxidation products and the gas phase is represented by air. The oxidation process can be carried out either in a reactor series or in a single reactor at least one of which is preferably equipped with at least two airlift-type trays. When specific CHP concentration is achieved, the oxidation products are discharged from the reaction zone and treated in a mixing device with aqueous ammonia or water to remove organic acids such as formic acid, benzoic acid, etc. and to remove phenol, which is an inhibitor of oxidation reaction. The cumene oxidation product stream, free of organic acids and phenol, is recycled to the same reactor in the case of single reactor, or is passed to the next reactor of the series in the case of reactor series. In all cases, the oxidation products treated with water or aqueous ammonia are first directed to a unit for separation of aqueous phase from organic products and then anhydrous organic product stream is forwarded to the next reactor of the series, or recycled to the single reactor for the continued cumene oxidation until the required CHP concentration is achieved.
The purpose of the present invention is to provide an advantageous method for accelerating the cumene oxidation reaction without the drawbacks of the above-described previously known approaches. Such a method is of great use in technologies as disclosed in the MPCH Application, as well as in other processes and process configurations where it is desirable to achieve a controlled acceleration of the cumene oxidation process without decreasing process selectivity, and without jeopardizing process safety.